European officials and business executives are quickly mobilizing a counter effort to the expected U.S. rebuff of the Iran nuclear accord, encouraging companies to invest in Iran while urging Congress to push back against White House moves that could hobble the deal. ZURICH —

The European stance — sketched out on the sidelines of an Iran-focused investment forum in Zurich this week — is an early signal of the possible transatlantic rifts ahead as the United States' European partners show no sign of following the White House call to renegotiate the landmark pact with Tehran.

"The nuclear deal is working and delivering, and the world would be less stable without it," Helga Schmid, the secretary general of the European foreign policy service, said in a speech at the Europe-Iran Forum.

This amounted to a warning shot that Washington may once again find itself isolated from key Western allies, who already broke with the White House over issues such as President Trump's call to withdraw from the Paris climate accord.

Trump plans to declare next week that the 2015 Iran deal — which curbs Iranian nuclear activities in exchange for sanctions relief — is no longer in the U.S. national interest, according to U.S. and European officials. Such a move would then give Congress 60 days to vote to reimpose sanctions.

This could pave the way for the deal's collapse, or more likely Europeans and others such as China and India could try to keep their growing economic and diplomatic engagement with Iran — with the United States on the outside looking in.

"The risk [of sanctions] is there, but my perception is that everybody outside the U.S. who participated in the deal wants to increase relations with Iran," Ulrich von Zanthier, director of financial risk management at KPMG, a global audit and advisory firm, told the conference.

If the United States reintroduces sanctions, "it is what it is," he said. "But at the moment, we can do business, so let's do business."

European diplomats and business leaders said they hope the 60-day period will provide them with a diplomatic buffer zone in which they can convince Congress to salvage the agreement.

"There's a period of 60 days where things need to work out in a way that upholds the [agreement] with the U.S. still in it," said a senior executive at a Europe-based multinational company who spoke on the condition of anonymity to discuss sensitive matters related to Iran sanctions.

"There's no real alternative" to the deal, the executive said, adding that "it's an illusion to think you can reopen and renegotiate."

The agreement, known as the Joint Comprehensive Plan of Action, was the result of years of negotiations between Iran and world powers. It was hailed as a victory for global diplomacy and nuclear nonproliferation and allowed Iran to resume oil exports and foreign companies to tap into a vast consumer market.

Since then, the International Atomic Energy Agency, the U.N. watchdog tasked with monitoring Iran's nuclear program, has repeatedly certified the country's compliance with the deal.

Still, the Trump administration has said the agreement does not go far enough in countering Iran's ballistic-missile program and support for groups that the United States considers terrorists, such as Lebanon's Hezbollah.

In one sign of possible openings to ease U.S. concerns, a Tehran-based Western diplomat said this week that European and Iranian officials already had begun discussions over Iran's ballistic-missile program and support for proxy groups in places such as Syria and Iraq.

"It will take time to make progress on those issues," the diplomat said. "But it's not a matter of bringing Iran back to the table for negotiations on those issues, because the discussion is ongoing."

Trump is expected to announce a major policy shift on Iran next week — one that will more aggressively target Iranian security services and push for more radical enforcement of the deal, officials say.

The deal has been "put into question in harsh terms by some in recent months," said Schmid, the foreign policy group chief, referring to the U.S. administration.

"As Europeans, we will do everything to make sure it stays," she added.

Iranian leaders also have insisted that the pact cannot be renegotiated. On Friday the head of Iran's nuclear agency, Ali Akbar Salehi, warned that Iran would be forced to abandon the accord if other countries followed the U.S. lead to possibly reimpose sanctions.

"But if the U.S. leaves the deal on its own with the others adhering to it, the situation will be different," Salehi told Iran's Fars News Agency.

Part of the European effort to save the deal includes reassuring European companies and banks that they have political support for their investments, even as some businesses have struggled to navigate Iran's volatile economy.

But for others, the risk may be too great.

Before the nuclear deal, the United States imposed what are known as secondary sanctions, under which the Treasury Department penalizes companies or people who do business with Iran. The fear is that the United States may revive those strict regulations — putting foreign companies doing business in Iran under the cloud of possible U.S. clampdowns.

"Iran is a big market. It's also quite a stable country," said the executive from the multinational company. But multinational companies "have to consider markets around the world, and Iran today is still relatively small compared to Europe or the U.S."